"Custom adding? Not sure what that means. My point is, the Quick Launch tool bar definitely is "available" in W10. You just have to enable it. While true, adding it back to the Toolbars options menu is not a one-click process, it is still easy and a one-time process. You don't need to edit the Registry, for example, or create folders or the Quick Launch folder itself. Why? Because it is already in there, and "available" to be added to the Toolbar options menu.
And no, you don't have to put a "self-made" folder anywhere. Did you follow that link I provided? The folder is already there. You are just telling the system where it is.
Here is another tutorial to show you it is easy to enable it.
And it is not about dealing with installer scripts since most current programs don't attempt to install shortcuts to Quick Launch. Once the Quick Launch tool bar is enabled, the user can simply drag and drop any shortcut to it.
What I might do, for example, is create a new shortcut to TPU on my desktop. Then simply drag that shortcut to Quick Launch and viola! I have a shortcut to TPU on Quick Launch that is NOT cluttering up my desktop. Piece of cake.
So yes, it does illustrate one of those "legacy functions". But it does it by already being available. Just because Microsoft has severed the direct connections (menu options) to it, that does not mean it is not available, or that it cannot easily be reconnected and added back to the menu.